This invention relates to an electronic part, for example, a contact for an electrical connector, lead frame or the like, and more particularly to a microelectronic part having a component portion, for example, terminal portion which is plated with solder or adapted to abut against a portion plated with solder, the electronic part being capable of preventing the flowing or wicking of the solder due to wetting toward another component portion, for example, a contact portion of the electronic part in a later process, for example, surface mounting process.
The term "wicking" as used herein is intended to designate the upward flowing of molten solder due to wetting, as if it were a melt wax rising along a wick with capillary action.
In many cases, terminals of a circuit board are electrically connected by means of soldering to electronic parts, for example, contacts of electrical connectors equipped on the board.
Such an electrical connector usually has contacts as connecting parts. In general, the contact is formed of a metal plate by means of punching, bending and the like. The contact portion of the contact is usually plated for electric contact to improve its corrosion resistance and electric conductivity. On the other hand, the terminal portion of the contact, which is formed continuously with the contact portion, is usually plated with a metal required for soldering in order to perform the reliable soldering or to improve the adhesion in soldering in a later process. The metal for plating the terminal portion is usually solder, but it may be gold (Au), palladium-nickel (Pd--Ni), palladium (Pd) or tin (Sn) as the case may be. This plated portion is referred to hereinafter as a "plated portion for soldering" or "portion plated for soldering".
There is disclosed in Japanese Patent Application Opened No. H5-82,201 opened on Apr. 2, 1,993 a formation of copper oxide film by treating copper or copper alloy by means of the anode oxidizing process using an acidic solution in order to prevent a solder bridge. In this known technique, using a phosphor bronze of 0.2 mm in thickness and 20 mm in width as a blank material, after application of masking tapes, photo-resist or rubber-like tapes onto partial portions of the blank material, the material is selectively plated to obtain a gold-plated belt-shaped portion having a 4 mm width and a solder-plated belt-shaped portion having a 10 mm width. Thereafter, masking tapes, photo-resist or rubber-like tapes are again applied onto required portions of the blank material and then treated by the anode oxidizing process to form the copper oxide film.
In the microelectronic part concerned with the present invention, however, such a process of the prior art is troublesome and time-consuming, which could not be practically used.
In a hitherto used contact of an electrical connector, the gold plating and plating for soldering have been separately applied to the contact and terminal portions of an electronic part. With miniaturization of electronic appliances, however, electrical connectors have also been required to be miniaturized and hence the contacts used therein have also been miniaturized.
The present invention is directed to a microelectronic part of which length is of the order of several mm.
Consequently, with such a small sized contact having a gold-plated portion and a plated portion for soldering separately applied, a problem arises with the operation for electrically connecting the terminal portion of the contact to a terminal portion of a circuit board, for example, with the surface mounting technique. In more detail, the molten solder from the circuit board and the solder-plated portion of the contact would flow and rising (the so-called "wicking") in extreme case through the terminal portion of the contact to the contact portion, so that the flowing solder will contaminate the gold-plated contact portion of the contact.
In order to overcome this problem, it have been found that a nickel layer provided between the gold-plated contact portion and the terminal portion plated for soldering can prevent the flowing or wicking of molten solder toward the contact portion due to wetting in the surface mounting process, and the application of such a nickel layer has been practically used.
In this case, it is needed for the nickel layer to have a width sufficient to prevent the flowing and wicking of the molten solder due to wetting. With a miniaturized contact, for example, of the order of 5 mm in overall length, however, it will become to difficult to provide a nickel layer having a width sufficient to prevent the flowing or wicking of molten solder due to wetting in a reliable manner, because of its extremely narrow space. Therefore, the performance of the nickel layer for preventing the flowing and wicking of solder could not be effectively utilized.